Window sash locks.
Sweep locks are well-established mechanisms for locking together upper and lower sash of a window. They use pivotally mounted cams interlocking with cam receivers, and the cams and receivers are mounted on adjacent check rail regions of lower and upper sash. When a sweep lock is locked, it prevents the upper sash from lowering or the lower sash from raising; and it also tends to hold the confronting check rails or meeting rails of the upper and lower sash together.
Sweep locks can also be applied to sash that slide horizontally within a window. This changes the orientation of the sweep lock and the sash, because the lock is applied to overlapping but vertically extending sash elements. The window industry generally retains the terms xe2x80x9ccheck railsxe2x80x9d or xe2x80x9cmeeting railsxe2x80x9d for the overlapping elements of horizontally sliding sash, even though the vertical orientation would suggest that such elements might be called stiles.
Throughout the following explanation of the invention, it should be understood that a sweep lock can be applied to either vertically moving or horizontally moving sash. This leads to orientation of the sweep lock and its components in an xe2x80x9cuprightxe2x80x9d way as described in this specification when applied to horizontally extending check rails of vertically moving sash and in a xe2x80x9csidewaysxe2x80x9d way when mounted on the vertical check rails of horizontally sliding sash.
I have learned from wind force experiments that a conventional sweep lock leaves a window vulnerable to large pressure differences caused by high velocity winds. Subjecting windows to destructive wind force has shown the check rail region to be a zone of weakness. Negative wind force, for example, causing check rails to bow outward, which can happen during a wind storm, can shatter both of the window sash, in spite of a locked sweep lock. This can also lead to a conventional sweep lock becoming unlocked, which facilitates window failure.
This discovery has led to an improved sweep lock that more firmly locks together check rails of a pair of sash. My improved sweep lock more strongly resists tilting or angular separation of check rails as they are bowed outward in response to a negative wind force, and this significantly strengthens the check rail region and enhances the ability of a pair of window sash to survive a wind storm.
My wind-resistant sweep lock uses a locking cam that locks against an upward facing projection of a cam receiver while also locking against a downward facing projection of the cam receiver so that spaced-apart upward and downward locking between the cam and the cam receiver strengthens the locking of the check rails. Such a double upward and downward interlock between the cam and the cam receiver creates a locking moment arm that resists angular separation of confronting faces of the upper and lower sash check rails. In other words, such a double locking more effectively resists tilting of the check rails away from vertical, or from each other, in response to wind force. This in turn significantly strengthens the check rail region of the window and allows the window to survive in tact while subject to large negative wind force.
While working out an efficient way of structuring and mounting a sweep lock to achieve these advantages, I have also discovered an especially effective mount for the locking cam of a sweep lock. The mount is inexpensive, assures a convenient subassembly of cam lock and mount, and also provides uniform frictional movement of the cam lock during operation.